You can use the following patterns to specify the expression you want to search for:

+	Search for articles that contain all the specified keywords;
|	Search for articles that contain at least one of the specified keywords;
-	Search for articles that do not contain specified keywords;
""	Search for articles that contain the exactly specified phrase;
*	Search for articles that contain keywords parts

Example:
Outpost | Firewall +protection - finds articles that contain either 'Outpost' or 'Firewall' and 'protection'
Install* troubleshooting - finds articels that contain words beginning with 'Install' (Installation, Installer, etc.) and 'troubleshooting'
Note that search patterns are not case-sensitive.